Hardens TrustCACertFromBytes against the failure mode behind issue
#262 (corrupted /etc/pki/tls/certs/ca-bundle.crt on a SoundTouch 20)
and against silent transport-time corruption of our own writes.
Three-part change.
1. Atomic write path. The previous flow piped bytes straight into the
live bundle via `cat > <path>`; a dropped SSH session or partial
write left the device with a half-written trust store and no way
to roll back. The new path:
- uploads to <bundlePath>.aftertouch.tmp (sibling on the same
filesystem, same rw remount),
- reads the tmp back over SSH,
- validates the readback at the PEM-frame layer + the AfterTouch
sentinel bracketing,
- atomically `mv`s the tmp into place,
- on any verification failure: `rm -f` the tmp; the live bundle
is never touched, so there is no rollback semantics to reason
about.
The .original backup written on first install stays as
defense-in-depth (manual recovery for corruption from outside this
code path), but it is no longer the primary safety net.
2. New validators in pkg/service/setup/ca_validation.go.
- validateCABundleBytes: BEGIN/END marker counts match, every
decoded block is a CERTIFICATE with a non-empty body, decoded
block count equals BEGIN-marker count (catches a block with
unparseable base64 body), trailing non-PEM/non-comment content
rejected.
- validateAfterTouchLabelBracketing: CALabel appears exactly
twice and brackets exactly one CERTIFICATE block.
- stripAfterTouchEntries: collapses any number of stale
AfterTouch entries from the existing bundle. Older releases
reported to have appended without stripping, so long-lived
devices can carry several copies; we strip them all and log
the cleanup count rather than failing validation. Unpaired
sentinels (truncated prior install) surface as a structured
anomaly the caller logs and warns about.
The validators stay at the PEM-frame layer on purpose — an
earlier iteration called x509.ParseCertificate per block and
rejected the real ST20 bundle on block 29 (Go 1.23+ disallows
negative serial numbers, but Mozilla CCADB still ships ancient
CA roots that have them). Shipping that version would have made
every legitimate speaker install fail. The corruption mode #262
surfaces at the PEM-framing layer; x509-level checks aren't what
we needed.
3. testdata/ca_bundle_st20_pristine.crt is the pristine
/etc/pki/tls/certs/ca-bundle.crt captured off a real SoundTouch 20
(firmware 27.0.6.46330.5043500, snapshot 2022-08-04). Mozilla
CCADB public dataset, 165 certs, ~251 KB. TestValidateRealSpeakerBundle
locks in the cert count and asserts the strip pass is a no-op
against a bundle that has never been touched by AfterTouch.
Test infrastructure. mockSSH (both the setup-package and the
handlers-package copies) now mirrors UploadContent into a private
map so a subsequent `cat <path>` on the same path returns what was
written there. Lets the tmp-readback step in TrustCACertFromBytes
work against tests that only scripted the live-bundle path, without
per-test wiring. Two new behavioural tests in setup_test.go:
TestTrustCACert_StripsMultipleStaleEntriesSilently (pins the
multi-entry cleanup contract) and
TestTrustCACert_PostUploadVerificationFailureCleansUpTmp (pins the
rollback-free recovery: live bundle untouched, tmp removed).
Refs #262.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Tobias GesellchenandClaude Opus 4.7